Document: SAA-3-29-16

Effects of light and fertilizer addition on the invasive shrub Clidemia hirta (Melastomataceae).

DEWALT, S.J.* and K.ICKES

Louisiana State University, Baton Rouge, LA 70803 ¹

Abstract:
Clidemia hirta is a shrub native to tropical America where it grows in partially to completely open habitats, and it is an aggressive invader of both open and shaded areas where it has been introduced in Hawaii. We examined the hypothesis that differences in soil nutrient levels might affect the growth of this species in different light environments. At La Selva Biological Station in Costa Rica, we grew rooted cuttings of C. hirta in pots filled with alluvial soil on tables covered with different levels of shade cloth to achieve irradiance levels of 15, 25, 50, 70, and 100% full sunlight. Timed-release 15-13-13 fertilizer was applied twice to half the pots in each shade level. Fertilized plants had higher total biomass, leaf area, and relative growth rates than non-fertilized plants when grown at > 25% full sunlight. However, C. hirta grown at 15% was unresponsive to fertilization. Within each fertilizer treatment, plants grown at irradiance levels higher than 50% full sunlight had similar relative growth rates and total leaf area. Maximum photosynthetic rates were highest for plants grown in full sun regardless of fertilizer level but were similar among plants grown at < 75% full sunlight. These results suggest that soil nutrient levels do not affect the ability of C. hirta to invade shaded areas, but may affect invasion in high-light habitats.

Keywords: Costa Rica, invasive species, light, soil nutrients

This abstract is being presented at: 10:30 AM in session:
Poster Session #1: Light Relations.